RTV silicone rubbers which have crosslinked in the presence of moisture are easy to handle and have improved weathering and electrical properties. On account of these advantages, they find use in a variety of applications, for example, as sealants for plumbing fixtures (in kitchens and bathrooms), sealing materials in building and construction fields, and adhesives in electric and electronic fields. Among others, oxime-elimination type RTV silicone rubbers are utilized in a wider variety of applications since they remain firmly bonded to various members in wet conditions and are fully weather resistant.
As the house building technology improves these years, houses become more air-tight. Moist places in such houses are good habitats for microorganisms such as bacteria and mildew (fungi). Especially, fungi often grow on RTV silicon rubber while extending their hypha into the rubber interior. The resulting mildew is difficult to wipe off and remove even with chemical agents, detracting from the outer appearance of rubber.
One effective solution is to incorporate antibacterial agents into sealing materials. Illustrative known approaches taken for silicone sealing materials from the antibacterial and safety standpoints include the addition of 2,3,5,6-tetrachloro-4-methylsulfonylpyridine. 2-(4-thiazolyl)benzimidazole and N-substituted benzimidazolyl carbamate derivatives as disclosed in JP-A 51-106158, U.S. Pat. No. 4,247,442, and JP-A 56-38348, respectively. Sealing materials containing these compounds, however, will yellow upon application of heat or exposure to UV radiation. This yellowing problem prevents the amount of such antibacterial agents added from being increased to such an extent as to be effective for controlling the growth of all species of fungi.
U.S. Pat. No. 6,008,290 discloses an organopolysiloxane composition comprising a triazolyl group-bearing mildewstat. This composition is fully mildew resistant, but insufficiently antibacterial.
Also, JP-A 7-76654 discloses the combined use of an organic mildewstat and an inorganic antibacterial agent. This combination is effective for controlling bacteria and mildew, but unsatisfactory with respect to discoloring.
In connection with the problem of colon bacterium O-157 and the recent development and marketing of antibacterial products such as floors and sanitary ware treated to be antibacterial, the sealing materials used in such products are also required to be antibacterial.
There is a strong desire to have a sealing material which is endowed with high antibacterial and mildew resistant properties without a loss of quality such as discoloration, while maintaining safety.